The mammalian heart is an organ made up of four muscular chambers that function together to pump blood throughout the body. Each of the four chambers has an associated downstream one-way valve made up of movable, coapting leaflets or cusps which cooperate to prevent the backward flow of blood, or regurgitation, into their respective chambers. Two such heart valves, the aortic and pulmonary valves, also commonly known as the semilunar valves, are characterized by three leaflets or cusps 91. The aortic valve leaflets 91 are attached within the aortic root 90, usually to a tri-scalloped or triple scalloped line of collagenous, fibrous tissue generally referred to as the valve annulus 92. As such, a three-pointed crown-like structure serves to support the aortic valve cusps or leaflets 91. The U-shaped convex lower edges of each leaflet are attached to, and suspended from, the base 97 of the aortic root 90, with the upper free edges or margins 93 of each leaflet being free to move and project into the lumen of the aorta 99. Two adjacent leaflets approach one another at one of the three points of said crown-like structure to define a commissure 95 of the aortic valve. Behind each leaflet 91, the aortic vessel wall bulges outward, forming a pouch-like dilatation known as the sinus of Valsalva 98. In the region located slightly above the level of the commissures 95, the aortic root 90 creating the sinuses of Valsalva 98 merges into the substantially tubular portion of the ascending aorta 99 at a substantially planar transition zone commonly known as the sinotubular junction (STJ) 100. The aortic root 90 houses the aortic valve structures and generally includes the portion of the native aortic conduit extending form the left ventricular outflow tract (LVOT) to the portion of ascending aorta 99 slightly above the sinotubular junction (STJ). Typically, aortic root reconstructions or interventions usually involve the aortic valve, while ascending aorta interventions usually exclude the aortic valve and involve the native aortic conduit located generally downstream of the sinotubular junction. In some patients, one or two of the native valve cusps may be congenitally fused and a bicuspid or, more rarely, a unicuspid aortic valve may present.
Aortic root dilation is one of the most common causes of aortic valve incompetence in North America. Prevalence of surgical corrections for this pathology has increased considerably during the last two decades. There are a variety of surgical corrections (for example the Reimplantation technique popularized by David, or the Remodelling technique popularized by Yacoub) that have been developed over the years to surgically repair an aortic valve or reconstruct the aortic root portion of the ascending aorta. In most surgeries, especially conservative aortic valve surgery which restores valve competence in regurgitant aortic valves having occurred from a dilatation of the aortic root or a retraction of valve cusps, surgeons must assess the amount of dilatation in the aortic root and the size of native cusps in order to inform the reconstruction of said structures. Currently, calibrated cylindrical sizers such as Hegar dilators, or calibrated prosthetic valve sizers used to measure native valve annulus prior to implanting a prosthetic valve, are used. Such instruments are limited in their use in that they can only measure the internal diameter of the aortic root (schematically illustrated in FIG. 5, and labelled AA at the base of the aortic root and STJ at the level of the sinotubular junction). To measure, for instance, the geometric height of the valve cusp 91 (i.e. the distance between nadir 96 and nodulus of arantius 94) a ruler or scale that is usually not sized or configured appropriately for measurement of valve cusps, must be used in a second separate set-up, once the Hegar dilator is removed from within the aortic root to visually expose the valve cusp. Measurement of the distance between commissures 95 is also challenging since the aortic root 90 is not pressurized and does not retain its substantially tubular geometry especially when aneurysmal sinuses of Valsalva 98 have been resected leaving behind a scalloped aortic root.
There is room for improvement in providing a surgical tool or instrument that can measure the internal diameter of the aortic annulus 92 at the virtual basal ring 102 location, or the aortic root diameter AA, and simultaneously also visually assess and measure the geometry of the valve cusps while said tool or instrument remains inserted within the aortic root. As such, the spatial relationship of the native aortic structures may be assessed and measured. Such measurements obtained by said surgical tool are useful in informing the surgeon of the extent of surgical reconstruction required to be performed on the aortic root or aortic valve contained therein.
Accordingly, there exists a need for a measuring tool or implement for use in valve surgery that can provide the following benefits: i) measurement of at least one of the internal diameters of the aortic root, aortic annulus, basal ring diameter or sinotubular junction, ii) geometric height of the valve cusp (dimension between the nadir and nodulus of arantius), iii) height of the commissure (dimension from the basal diameter of the aortic root to the commissure peak), iv) angle between two commissures, and v) circumferential length between two commissures.
It is also a further advantage if the surgical tool can also have additional functions to size or tailor a prosthetic aortic conduit in conservative aortic valve surgeries where the native valve cusps are preserved, but there exists the need to replace aneurysmal aortic root tissue, such as the Sinuses of Valsalva, or an aneurysmal ascending aorta with a tailored prosthetic conduit.